Multiple input multiple output (MIMO) systems enable high speed wireless communications by concurrently transmitting a plurality of NSTS data streams using a plurality of NTX transmitting antennas at a transmitting station. The concurrently transmitted data streams may be received at a receiving station using a plurality of NRX receiving antennas. The IEEE 802.11n specification contains specifications for the use of MIMO systems in wireless local area networks (LAN).
In wireless LANs utilizing multiple transmit antennas, the radiating power for signals transmitted by a transmitting station may be limited by a total-power constraint or a per-antenna power constraint, or a combination of the two. A total-power constraint may set an upper limit on the total radiating power across all transmitting antennas at a transmitting station, while a per-antenna power constraint may set an upper limit on the radiating power emitted from any single antenna at the transmitting station.
A total-power constraint usually results from regulations governing a given geographical region and/or frequency band. The total-power constraint may be represented by a maximum total-power level parameter, Ptotal. A per-antenna power constraint usually results from limitations in the radio transmitter circuitry at the transmitting station (for example, a power amplifier may create unacceptable levels of distortion when the radiated power level from a given antenna exceeds the per-antenna power constraint. The per-antenna power constraint may be represented by a maximum per-antenna power level parameter, Pmax. Depending on the capabilities of the transmitting station and/or applicable regulations, one or both of these constraints may apply for communication between wireless devices, for example communicating stations in a wireless LAN. Some popular wireless LAN standards are designed to operate under a total power constraint and may perform poorly when operating under a per-antenna power constraint.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.